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<h4 class="heading"><span class="type">Paragraph</span></h4>
<p>For the Delta function, we may understand it in the sense of limit. Define a sequence of functions</p>
<div class="displaymath process-math" data-contains-math-knowls="">
\begin{equation*}
d_{\tau}(t)=\begin{cases}
1/(2\tau),\quad - \tau&lt;t&lt;\tau,\\
0,\quad t \leq -\tau ~\mathrm{or} ~t \geq \tau,
\end{cases}
\end{equation*}
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<p class="continuation">where <span class="process-math">\(\tau\)</span> is a small positive constant (see the illustration of <span class="process-math">\(d_{\tau}(t)\)</span> in Figure <code class="code-inline tex2jax_ignore">[cross-reference to target(s) "Fig2_1" missing or not unique]</code>).</p>
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